^^^る and cursive 子 look very similar. The reason I assume it's 子 is because it fits Shamiko's name (Shamiko is シャミ子 and Yuko is 優子, both have 子) This is an example of a cursive 子
All of this does not really explain what the point is though. Why write ko on her face in the first place? I dont see the connection to either hanetsuki or the year of the rat.